There are a number of applications in which it is of interest to determine whether or not a person's eyes are open or closed as well as the amount of time that the eyes are open/closed. One such application is the detection of drowsiness in the operator of a motor vehicle, such as but not limited to the driver of an automobile or the like (e.g., a truck, etc., but also including airplanes, trains, etc.).
Prior art techniques have been developed to detect and monitor a person's eyes. Some of these techniques rely on the detection of light reflected off of the eye(s) of a subject. However, these techniques generally have one or more disadvantages that limit their use in motor vehicles. One disadvantage is their inability to provide reliable data. Another disadvantage is that they are typically invasive or distracting to the subject. For example, they may distract the subject while in operation, or it may be necessary for the subject to wear special equipment. Prior art techniques are also relatively complex in their setup and operation, perhaps requiring multiple specialized detectors and/or beam splitters, and perhaps requiring precision alignment of each of these parts. As such, the cost of prior art systems may be relatively high. If manufacturers and the public are to embrace drowsiness detectors, it is desirable for the detectors to be relatively unobtrusive and inexpensive.
Another disadvantage to prior art techniques is that they do not perform well during the day. Under brighter ambient light, the light reflected from the subject's eyes is relatively dim and hence more difficult to detect. Accordingly, the prior art techniques are not able to operate as efficiently or reliably during the day. In addition, at night, other light sources (such as headlights, streetlights, etc.) can interfere with detection of the light reflected from the subject's eyes. Thus, prior art techniques may be problematic at night as well as during the day.
Another prior art technique for drowsiness detection may be generally referred to as a lane change detector. This technique looks at the surface of the road (more specifically, at features of the road such as lane markers) to determine if the vehicle is drifting into another lane or off the road. One problem with this type of technique is that not all roads have the features relied upon (e.g., lane markers may be absent). Another problem arises because once the change in lanes is detected, there will likely be an immediate need for corrective action. In other words, a lane change detector may not anticipate that a problem (e.g., inappropriate lane change) is occurring, and instead will alert the driver only after the problem has occurred. By the time the lane change detector infers that the vehicle is drifting out of its lane, the operator may already be asleep and thus may not have the faculties needed to take immediate and proper corrective action.